could not only open dialogs and windows but could also register come cleanup routine in the

CleanIO

.

runAndCleanup

would first run the opening actions and afterwards the required cleanup actions.

I.e. if the dialog was opened, the dialog must be closed, but not the window.
That is, the cleanup procedure depends on the outcomes of earlier actions.

Now consider the slightly different task, where functions shall register initialization routines
that shall be run before the actual action takes place.
(See the original discussion started by Michael T. Richter in Haskell-Cafe:
Practical Haskell Question)
This is impossible in the monadic framework.

Consider the example above where the choice between

openDialog

and

openWindow

depends on the outcome of

getLine

.
You cannot run initialization code for either

openDialog

or

openWindow

,
because you do not know which one will be called before executing

getLine

.

If you eliminate this dependency, you end up in an applicative functor
and there you can do the initialization trick.
You could write

2 Some advantages of applicative functors

Code that uses only on the

Applicative

interface are more general than ones uses the

Monad

interface, because there are more applicative functors than monads.

Programming with

Applicative

has a more applicative/functional feel. Especially for newbies, it may encourage functional style even when programming with effects. Monad programming with do notation encourages a more sequential & imperative style.